We can expect an abundance of cross-reactivity of Birch tree pollen, with other trees such as, the alder (Alnus glutinosa) - hazel (Corylus avellana) or hornbeam (Carpinus betulus) are examples, this year because of the changes in our environmental temperatures. Food cross-reactivity of Birch and apples are known, but..... there are many more. See your Dr. or Allergist for up-to-date information. Sue C. Killian wrote an excellent book about allergy and cross-reactivity.